Oil shale is a natural sedimentary rock containing an abundance of residual organic material which, when processed, can be made into oil and fuel products. Typically, oil shale, such as exemplified by the Green River formation in Wyoming, Colorado and Utah, has about 15-20% organic material embedded in an inorganic mineral matrix. The organic portion is composed generally of a soluble bitumen fraction an insoluble fraction in which kerogen constitutes the bulk of the insoluble organic material. The bitumen fraction is readily solubilized by organic solvents and can be removed for refinement by physical means. Th keorgen portion is characterized by its insolubility in organic solvents and is therefore more difficult to remove. In Green River oil shale, kerogen makes up about 75% of the organic components and in most all oil shale is the major organic component.
The inorganic mineral matrix in which the desired organics are trapped is composed primarily of carbonate materials such as dolomite and calcite, quartz and silicate minerals such as analcite or other zeolites. Several approaches have been used with oil shale for separating the organics from the mineral matrix. The usual process comprises crushing the matrix rock and subjecting the crushed matrix to heat in a retort to distill off the kerogen. Other processes involve erosion of the inorganics, for example, by acid leaching, to keep the organics intact. The kerogen component contains considerable quantities of nitrogen-, sulphur and oxygen-compounds, which contribute in large part to the high decomposition temperature for the kerogen and which produce significant pollutants during the usual retorting process. Attempts have been made to hydrogenate the kerogen fraction to remove these undesirable components and to upgrade the shale oil to more conventional petroleum characteristics. Since chemical reducing agents do not greatly affect the kerogen, extremely strong reducing conditions have been applied. Chemical reduction of kerogen has required high pressures and high temperatures (e.g., 4200 psig and 355.degree. C). Such drastic conditions increase the possibility for molecular rearrangements, limiting the desirability of this technique. The hydrogenation of solid fossil fuels such as coal, was accomplished by electrochemical means by Sternberg et al. in 1966. See in this regard, H. W. Sternberg et al., "Electrochemical Reduction in Ethylenediamine", Coal Science (R. F. Gould, Ed.) ACS Pub., Washington, D.C. 1966, Chapter 33. In that process, hydrogenation was conducted in ethylenediamine in the presence of lithium chloride under mild conditions (30.degree. C and 1 atmosphere) with an addition of 33 hydrogens per 100 carbon atoms and a decrease in sulfur content. The presence of large amounts of carbonates and silicates and general matrix configuraion of oil shale discourages application of such a reduction process to oil shale.
The present invention provides a means for recovering economic values of oil shale by electrolytic hydrogenation by first leaching the carbonate matrix from the shale and subjecting the resultant residue to reductive electrolysis. Leaching out the carbonate components develops the porosity and permeability of the residue, increasing the extent of its internal surface and providing an interconnected pore structure which aids in releasing the bridge portions of the kerogen (i.e., amides, cycloalkadines, esters, and heterocyclic compounds). The released bridge components of kerogen serve as proton-donors for further electrolytic refining. The reduced residue can be separated from the electrolyzed slurry, for example, by centrifugation, to yield an upgraded product. Electrolysis is preferably conducted at a current density above about 50 amperes per square meter of anode surface (50 A/m.sup.2)for a period of at least an hour, or for several days, if necessary, at low current density. A current density of up to 300 A/m.sup.2 can be used.